Answer:
The fourth dimension is a difficult concept to grasp because it cannot exist in our dimension in the first place. When you look at a straight line, it has 1 dimension, since there is only one axis. When you look at a flat plane like a tv screen or a computer monitor, it has 2 axises, x and y (x = left and right, y = up and down), and therefore is 2 dimensional. When you look at a cube, it has 3 axises, x, y, and z (x = left and right, y = up and down, z = forward and backward), and is therefore 3 dimensional. 3 axises is the highest amount that any shape can have in this universe, so thats why no matter how hard you think, you cant even conceive of a fourth dimension, but it would be basically having a whole new axis in which things can exist on. Hope this helps :)
Explanation: